Matrix and method of producing said matrix

ABSTRACT

The invention relates to a matrix suitable for use in the replication of a plastic element having a positive microstructure, comprising a first wear-resistant layer that is supported by a carrier element, wherein the matrix comprises a heating means for supplying electrical heat energy through the wear-resistant layer or carrier element. The invention further relates to a plastic element producing machine and a method for the manufacture of a plastic element having a surface with a positive microstructure.

This is a continuation application of application Ser. No. 09/554,530filed on Jul. 19, 2000 now U.S. Pat. No. 6,454,970, which is a 371 ofPCT/SE99/01858, filed Oct. 14, 1999.

FIELD OF INVENTION

The present invention relates to a method of producing a matrix that canbe used in a compression moulding, embossing, injection moulding and/orother plastic element-producing machine. In particularly the presentinvention relates to a matrix having a surface, or a part of saidsurface, which is provided with a negative microstructure that can bereplicated as a positive microstructure, on a surface of a plasticelement, such as a compact disc (CD) formed in such a machine.

The invention also relates to a matrix manufactured by said method, theuse of said matrix to form a plastic element and the plastic element soformed.

DEFINITIONS

In the following, the expression “positive surface structure” shall beunderstood to mean the surface structure (including topographic surfacefeatures such as microstructures or plane surfaces or parts of surfaces)that appears on a plastic element produced in a plasticelement-producing machine, and that by “negative surface structure” ismeant the inverse of the positive surface structure, i.e. the surfacestructure exhibited by a matrix used in such a machine.

By plastic composite is meant a curable mixture of polymeric materialand a filling material, where the filler is normally present in surplus.

There is defined in the following description a matrix first wearsurface that is formed on a first wear layer, and a matrix second wearsurface that is formed on a second wear layer.

The first wear surface is the surface of the matrix that carries amicrostructure and that faces towards the manufactured plastic element,while the second wear surface is the surface of the matrix, alsoreferred to as the rear side, which is preferably planar and lies inabutment with the corresponding planar support surface of a mould half.It will be understood that these latter two surfaces need notnecessarily be planar but that they shall connect with one another so asto be able to take-up forces generated during the moulding or castingprocess e.g. they can have complementary shapes.

DESCRIPTION OF THE BACKGROUND ART

In respect of replicating microstructures on plastic elements producedin a machine of the kind defined in the introduction, it is known toproduce first an original master in some suitable way, and then toproduce a matrix for use in said machine on the basis of this master.Matrices of this kind can be produced by coating a master or an originalthat has a positive microstructure on one surface with a metal layer ora metallic coating and removing the negative-microstructured metal layerfrom the master to thereby obtain a metal plate that can serve as amatrix in the compression moulding, embossing and/or injection mouldingpress. Normally each mould half can have its own matrix and a flowing,hot (approximately 400° C.) plastic mass is pressed under high pressureinto a delimited mould cavity formed by cavities in brought togethermould halves The flowing hot plastic mass is then allowed to solidify(at approximately 140° C.) between the brought together mould halvesbefore the mould halves are opened and the solidified element can bepressed out.

Lithographic processes, in particular lithographic processes that havebeen developed primarily for use in the micro-electrical field, are anexample of known methods for producing a master. One of these methods isbased on etching a semiconductor surface and/or depositing materialthereon. Other methods are based on the removal of parts of materialwith the aid of a laser, so-called laser ablation, with the aid oftraditional NC-machines, with the aid of precision-controlled,high-speed diamond millers, with the aid of electric discharge machining(EDM), wire EDM and/or some other suitable method.

Such originals or masters are normally produced from a material that ischosen to be suitable with respect to a given machining process.

In the case of lithographic processes, the material is most often asheet of silicon, glass or quartz, whereas in the case of laser ablationthe material most often used is a sheet of plastic composite and/or apolymeric material.

In the case of metal processing methods, plastics and soft metals mayboth be suitable.

It is well known that the requirements of a given replication process ona given material in the matrix and the plastic element are not the sameas the requirements that must be met with respect to the original or themaster. For instance, with respect to injection moulding of such plasticelements where one or more surface parts shall present a microstructure,one or both of the mould halves of the machine and the matrix usedtherein must be made of a stable material that can withstand the highpressures that occur during the course of manufacture, and which willnot be worn down unnecessarily quickly by the thermal and mechanicalwear-and-tear to which the mould halves and the matrix are subjectedduring the casting or moulding process.

It is known to produce such matrices, and primarily matrices for usewith microstructure, by transferring the shape and surface structure ofa master to a metal plate which can then serve as a matrix.

One manufacturing method is based on first producing a master on asurface of a glass plate, a semiconductor plate or a metal plate,coating the surface with a light-sensitive layer and exposing selectedsurface sections of this light-sensitive layer through the medium of alaser or the like, and washing and cleaning the selected surfacesections. A metal layer is applied to the exposed and cleaned surface ofthe master, through the medium of a sputtering process, a vapourdeposition process, and/or through the medium of a plating or claddingprocess, for the length of time required to form a metal plate. Themetal plate can then be removed from the master. The metal plate has afirst surface which exhibits a negative microstructure which is intendedto face towards the inside of a mould cavity. The metal plate can beused as a matrix after further machining, i.e. smoothing, of a secondsurface that faces towards the mould half in the machine.

It is this method that is presently used in the manufacture of a matrixused in an injection moulding press for the production of optical discs,e.g. CD discs.

Other ways of producing a matrix or a master include: an electricallyinsulating microstructured disc serving as a master or matrix can becoated with a thin metal layer by means of a sputtering process and/orby vapour deposition; an electrically conductive microstructured disc orlayer that functions as a master or matrix can be coated with a muchthicker metal layer by means of a plating or cladding process; a discintended to function as a matrix can be coated with a thin electricallyconductive layer, such as a nickel, silver, or gold layer or some likemetal layer, by means of a plating or cladding process.

It is also known to connect a metal layer electrically and to submerge adisc in a solution that comprises among other things, metal ions, and topass an electric current through the solution onto the disc or masterunit and therewith cause metal ions to precipitate as pure metal ontothe surface of the disc. In this way a structure can be produced inmetal that has the inverse function of the microstructure on the master.

It has been found that the above method can be readily applied inrespect of flatter structures, particularly when the depth of themicrostructure is limited to, or smaller than, about 0.2 μm.

It has been found that in forming a matrix the metal build-up on themicrostructure-carrying surface of a master results in minor defects orirregularities on the rear side of the matrix, which irregularities arecaused by the microstructure, and that it is necessary to subsequentlysmooth said rear side in order for it to lie in effective abutment, e.g.flat, on a flat surface on the mould half that supports it in thepressing machine used.

Practical applications have shown that in the case of deeper structuresin the master microstructure, the master pattern will be embossed on therear side of the matrix or metal plate.

Various procedures are known for reducing or eliminating this problem.

A first measure is to apply an extremely thick layer of metal by meansof a plating process or some equivalent process. The resulting platewhich is intended to serve as the matrix will be strong and stable. Theplate can then be placed in equipment in which the metallic rear side ofthe plate can be smoothed down or levelled mechanically, such as by agrinding, polishing and/or lapping process, while still retainingsufficient strength to serve as a matrix.

The process of applying a truly thick layer of metal as in the case ofdeeper microstructures takes a relatively long time to achieve, forinstance it will take from 10 to 20 hours to apply a nickel claddingwhich is a few millimetres thick.

Furthermore, it takes considerable time to grind and/or polish down themetallic rear side to a smooth surface. Moreover, the adhesion betweenthe master microstructure and the conductive metal layer in the matrixmust be capable of withstanding the tensions that are generated in theinterface therebetween.

The use of available grinding and/or polishing equipment for smoothingthe metallic rear side to a flat surface also requires the master to bevery stable.

Various methods are known to counteract the problem arising from adefective or irregular and uneven rear side, by applying differentplating processes so as to be able to level out the growth of the metallayer against a planar metallic rear side.

One known method in this respect uses a pulsed field instead of a directcurrent with constant field. However, in principle, a metallic layertakes longer to grow with a pulsed field than with a direct current.Using suitably adapted parameters and chemical compositions, this methodenables the deep microstructure parts to be coated and built-up morequickly than the shallower microstructure parts, meaning that the deepstructures will be overgrown and the metallic rear side will becomerelatively flat.

Practical experience has shown, however, that the metallic rear sidemust still be smoothed down, by grinding, polishing and/or lapping saidsurface.

With respect to the tine consumption of the two methods involving apulsed field and a constant field, the coating time in the first methodwill be longer than the coating time in the latter method, whereas thetime taken to smooth down said surface will be shorter in the firstmethod than in the second method.

When manufacturing plastic elements with a positive surface relatedmicrostructure, different means and arrangements are known for supplyingthe matrices belonging to the mould halves, and consequently thematrices in general, with alternating heating and cooling.

Heat is applied in order to thereby make the composite plastic or theplastic material used more easily flowing against the surface of thematrix in order to in this way be able to improve the replicating of themicrostructure.

It is also known to apply cooling, such as a cold fluid, in the form ofoil or water, or gas, in the form of air, to the mould halves of thematrix in order to thereby, immediately after the finishing of themanufacturing process in the machine, to, via the matrix, cool theplastic element down to the solidification temperature so that thepositive surface structure belonging to the plastic element remainsintact.

It is herewith obvious that because of the matrices' and the mouldhalves' large heat storing capacity, large heat and cooling transportsystem are required, which lead to a consequently slow manufacturingspeed.

Since the manufacturing speed is extremely dependent on the time takento heat up the matrix surface, by a heat supply to the mould halves,during the injection process and the time for a subsequent cooling ofthe cast element via the matrix surface and the mould halves, differentmeasures have been suggested.

Thus, it has been suggested to form channels in the mould halves andsupply hot water respectively cold water through these, but because ofthe high pressure which exists inside the mould cavity it is technicallydifficult to position them optimally close to the matrix.

With the intention of further reducing the cycle time it is previouslyknown to use a heat insulating layer between the matrix and the mouldhalves (see—Optimizing Pit Replication Through Managed Heat Transfer—byThomas Hovatter, Matthew Niemeyer and James Gallo, published by GEPlastics, Pittsfield, Mass. USA).

SUMMARY OF THE PRESENT INVENTION

Technical Problems

When taking into consideration the technical deliberations that a personskilled in this particular art must make in order to provide a solutionto one or more technical problems that he/she encounters, it will beseen that on the one hand it is necessary initially to realise themeasures and/or the sequence of measures that must be undertaken to thisend, and on the other hand to realise which means is/are required insolving one or more of these problems On this basis, it will be evidentthat the technical problems listed below are highly relevant to thedevelopment of the present invention.

When considering the present state of the art as described above, itwill be evident that a technical problem resides in providing a simplemethod of producing a matrix that can be adapted for use in acompression moulding, embossing and/or injection moulding press, wherethe matrix is provided on one surface with a negative microstructurethat can be replicated in the machine as a positive microstructure on asurface part of a produced plastic element, through the medium of aplastic composite or plastic material, and therewith obtain aninexpensive matrix that has a sharply defined microstructure.

Another technical problem is one of providing with the aid of simplemeans conditions that will enable the matrix to be given amicrostructure-related first wear-resistant surface formed on a firstwear-resistant layer which has an adaptable and relatively high abrasionresistance.

Another technical problem is one of providing with the aid of simplemeans and measures conditions which will enable the matrix to bebuilt-up of at least two layers, a thin first wear-resistant layerpresenting said microstructure-related surface, and a layer whichstiffens or reinforces said thin wear-resistant layer, this latter layerbeing a thicker layer and which is referred to hereinafter as thecarrier element.

Still another technical problem is one of providing with simple measuresconditions that will enable the material used in the first thin layerand the material used in the thick layer or carrier element to be chosenwith such properties and/or thicknesses as to fulfil predeterminedrequirements and conditions.

Another technical problem is one of realising the significance of andthe advantages that are gained with enabling the matrix to be producedby metal coating, with the aid of a metal coating process, a master thathas on one surface a positive microstructure, and coating this thinmetal layer with a plastic composite so as to form said carrier element

Another technical problem is one of producing with simple means andmeasures a matrix which is formed substantially or exclusively from aplastic composite and which can be used in a machine, where the timetaken to produce the matrix from a master has been considerablyshortened, among other things by being able to eliminate or at leastsubstantially reduce the time taken to form on the plastic composite aflat rear side of the matrix for close abutment of said rear side withone of the two mould halves of said machine.

Yet another technical problem resides in realising the significance ofproducing the matrix from a master and to apply to the surface-carriedpositive microstructure a thin metal layer and to permit said metallayer to show on the rear side of the microstructure irregularities thatcorrespond essentially to said microstructure, and to realise theadvantages of filling said irregularities with a supportive plasticcomposite which, when cured forms a supportive sheet-like carrierelement, instead of building up the entire matrix with a thick metallayer.

Another technical problem is one of realising the significance offilling-out said irregularities with a chosen plastic composite andforming the carrier element in a special mould cavity.

Still another technical problem is one of realising the significance ofand the advantages gained by, forming said plastic composite, andtherewith said carrier element, from a mixture of plastic material orpolymeric material and a filler material such as quartz-filled ormetal-filled epoxy or silicone polymer.

Another technical problem is one of realising the significance of, andthe advantages that are gained by, using a plastic composite andtherewith a carrier element that has a coefficient of linear expansionand/or a thermal conductivity and/or a heat capacity that is adapted fora given process carried out in the machine, and also to the design ofsaid machine.

In respect of this application, a technical problem resides in utilisinga specially selected curing process so as to impart to the chosenplastic composite a hardness and/or hardening time which is dependent onthe application concerned, by applying heat to chosen parts of theplastic composite or plastic mass and/or irradiating the plasticcomposite or said mass with UV-light, or by using a bicomponent plasticcomposite.

Still another technical problem is one of realising the significance ofproviding a first wear-resistant layer and/or a metal layer thin, and toselect a plastic composite, and therewith a carrier element, that has alow heat transfer capacity so that the plastic mass pressed through themachine and between the mould part will be kept warm.

Another technical problem is one of realising the significance of andthe advantages that are gained and the dimensioning rules required withrespect to the application of a second wear-resistant layer on thecarrier element surface distal from the microstructured surface of saidmetal layer.

Another technical problem is one of realising the significance offorming said second wear-resistant layer from a material that has lowfriction qualities against the flat surface of said mould half and highabrasive resistance, such as titanium nitride or diamond-like-carbon(DLC).

Still another technical problem is one of realising the significance ofapplying said thin metal layer to said master or original when saidoriginal consists of an electrically non-conductive material, by meansof a sputtering process and/or by means of vapour deposition, andapplying said thin metal layer by means of a metal plating process whensaid material is electrically conductive.

Another technical problem is one of choosing the thickness of the metallayer within predetermined limits on the basis of the applicationperformed in the injection moulding press.

Still another technical problem is one of realising the significance ofand the advantages that are to be gained by creating conditions such asto greatly simplify smoothing-down of the rear side of the matrix and ofthe carrier element and/or totally eliminating the need of suchsmoothing.

There is a technical problem in, in a machine, for the manufacture ofplastic elements, being able to form an arrangement which with theminimal possible application of energy shall be able to keep thenegative surface structure of the matrix hot during the moulding processand thereby ensure a complete filling of the mould cavity before theplastic element is cooled.

There is furthermore the technical problem of how, with the help ofsimple means and measures, the cycle time can be reduced for themanufacturing of an element in a machine of the type mentioned in theintroduction.

There is also a technical problem within a machine for the manufactureof a plastic element, to be able to form an arrangement which with thesmallest possible application of energy is able to quickly cool thenegative outer structure of the matrix to a temperature correspondingwith and somewhat under the solidification temperature for the plasticmass.

It is a technical problem to, with simple measures, be able to form suchconditions within the matrix that a desired heating during the mouldingsequence takes place inside the matrix and that the heated matrix servesas a barrier against a cold mould half and that a desired cooling occursonly through simply disconnecting the heating sequence.

It should moreover be seen as a technical problem to be able to arrangeconditions in order to achieve an electrically controlled heating of thenegative surface structure of the matrix.

There is in this connection a further technical problem in at withsimple measures and with the use of one or more layers belonging to thematrix being able to offer a simple and, if necessary, even locallyacting heating in order to in that way be able to increase thereplication capability.

It is moreover a technical problem to, via a matrix related arrangement,be able to form a locally acting intensive heating in order to withinthe selected localities belonging to the mould cavity be able to offer abetter filling capability.

Then there is also a technical problem in for this purpose being able toprovide simple means and actions whereby an application of electricalheat energy to the whole of the matrix's surface structure can bepresented and furthermore, when necessary, a locally acting increasedapplication of electrical heat energy can be offered.

Then there is a technical problem in, with simple means, being able toprovide such conditions that said electrical heat energy shall be ableto be applied, via, or immediately beside, the negative surfacestructure belonging to the matrix, through applying a voltage to one andthe same layer for an adapted current distribution within said layerwhich can be conducting or semi-conducting.

There is a technical problem in with simple measures being able to formconditions for being able to offer a varying heat production, which onlythrough selecting the thickness for a conducting or semi-conductinglayer with a thinner layer for a higher heat production and vice versa.

Then there is a technical problem in with simple means being able toform such conditions that said electrical heat energy and its localdistribution shall be able to be applied, via or immediately beside, thenegative surface structure belonging to the matrix through applying avoltage to two adjacent conducting layers for a current distributionwithin an intermediate semi-conducting layer.

It should be seen as a technical problem to with simple measures be ableto form conditions for a varying heat production through selectingthinner thickness and/or lower conductivity in delimited surface regionswhere a higher temperature is desired and vice versa.

There is also a technical problem in being able to realise thesignificance of and the advantages connected with using said layerhaving a negative surface structure and/or a layer supporting this layerwhen the latter consists of an electrically conducting or electricallysemi-conducting material.

There is also a technical problem in being able to realise thesignificance of selecting the layer having the negative surfacestructure belonging to the matrix from a material, normally a metalmaterial, with a resistivity of between 0.025 and 0.12 (ohm×sq mm/m).

There is also a technical problem in being able to realise thesignificance of and the advantages related to allowing the layer havingthe negative surface structure belonging to the matrix be supported by alayer with a resistivity of 0.03 and lower.

There is also a technical problem in being able to realise thesignificance of and the advantages connected with allowing one or moresupporting layers to be made of a heat producing layer such as anelectrically conducting polymer.

It should especially be seen to be a technical problem to be able torealise the significance of the advantages related to that at least one,of a plurality of available layers, is selected to have differentthicknesses, thicker at a section which requires lower heat energy andthinner at a section which requires higher heat energy.

The present invention specially relates to an application where thelayer having the negative surface structure relating to the matrix is inthe form of a microstructure and therewith being able to realise thesignificance of allowing the heat production be adapted at selectedcross-sections to be higher than at other surface sections, in order toin this way similarly increase the replication accuracy and mouldfilling.

There is also a technical problem in being able to realise thesignificance of and the advantages related to allowing the heat energybe applied to a circular disk through applying a voltage between aperipheral surface part of a selected layer and a central hole.

Furthermore it should be considered to be a technical problem in beingable to realise the significance of allowing the electrical heat energybe applied to a circular disk through the application of voltage to aperipheral surface part for different layers with low resistivity and byheat production within an intermediate positioned layer with a highresistivity.

Solution

With the intention of solving one or more of the aforesaid technicalproblems, the present invention takes as its starting point a method ofproducing a matrix that includes on one surface a negativemicrostructure which can be replicated in an injection moulding press asa positive microstructure on a prepared plastic element, from a plasticcomposite or a plastic material.

The invention is based on the concept of enabling said matrix to beproduced by covering a master or an original that has a positivemicrostructure on one side thereof with a layer of covering material.

It is now proposed in accordance with the invention that there isapplied to the positive microstructure on the surface of said master athin wear-resistant layer that functions as a first wear-resistantsurface, said layer presenting irregularities that correspondessentially to said microstructure, and then filling-out saidirregularities with a plastic composite, such as to form a carrierelement or backing element for said first wear-resistant layer.

By way of proposed embodiments that lie within the scope of theinventive method, it is proposed that said plastic composite is appliedto level out said irregularities in a mould cavity.

It is also proposed that the plastic composite, and therewith thecarrier element, is comprised of a polymeric material and a fillermaterial, such as quartz-filled or metal-filled or carbon fibre-filledor other fibre- or particle-filled epoxy polymer or silicone polymer.

It is also proposed that the plastic composite, and therewith thecarrier element, have a coefficient of linear expansion and/or a thermalconductivity and/or a heat capacity adapted for a given process carriedout in a machine and also to the design of said machine.

It is also proposed that the plastic composite is cured in a mannersuitably adapted for injection moulding, such as by applying heat and/orirradiation with UV-light.

The plastic composite may also be a bicomponent composite.

It is also proposed in accordance with the invention that a plasticcomposite, therewith the carrier element, located beneath a hardwear-resistant layer serving as a first wear-resistant surface has anadapted thermal conductivity and/or an adapted heat capacity so that theplastic mass pressed forwards in the machine can be kept warn whileachieving short cycle times at the same time.

It is also proposed in accordance with the present invention that theplastic composite, and therewith the carrier element, can be coated witha second wear-resistant layer on the surface that lies distal from thefirst wear-resistant surface, so as to reinforce the matrix constructionagainst abrasive wear.

This second wear-resistant layer may be comprised of titanium nitrate orDLC.

It is also proposed in accordance with the invention that said thinfirst wear-resistant layer is comprised of a metal layer and that saidmetal layer shall be applied by a sputtering process and/or a vapourdeposition process, or a metal plating process.

It is also proposed that the thickness of the first wear-resistantlayer, such as the metal layer, is carefully chosen with respect toapplication and with respect to the design of the injection mouldingpress.

The invention also provides a matrix, which is adapted for use incompression moulding machine, an embossing machine and/or an injectionmoulding press.

It is particularly proposed in accordance with the invention that themicrostructured surface of the matrix shall be comprised of a thin,first wear-resistant layer, such as a metal layer, and that said firstwear-resistant layer is preferably supported by a carrier element.

In accordance with proposed embodiments that lie within the scope of theinventive concept, the carrier element is conveniently comprised of athick plastic composite layer.

In this regard, it is proposed that the carrier element be comprised ofa plastic composite comprised of a polymeric material mixed with afiller material, such as a quartz-filled or metal-filled or other fibre-or particle-filled epoxy polymer or silicone polymer.

It is also proposed that the carrier element will be comprised of aplastic composite that has a coefficient of linear expansion and/or athermal conductivity and/or a heat capacity adapted to a chosen processand to a chosen design of the injection moulding press.

It is particularly proposed that the carrier element is comprised of aplastic composite that can be cured by applying heat and/or irradiatingsaid composite with UV-light. Alternatively, the plastic composite maybe a bicomponent composite.

The carrier element and the thick plastic composite layer may also becomprised of a plastic composite that has a pronounced low thermalconductivity e.g. less than 2 W/m/°K.

It is particularly proposed that the carrier element can bestrengthened, primarily from an abrasion aspect, for instance with theaid of a second wear-resistant layer on the surface distal from themetal layer surface. This reinforcing second wear-resistant layer may becomprised of titanium nitride or DLC in this case.

It is further proposed that heating means be provided for supplying heatenergy to said matrix.

It is also proposed that said heating means should be formed by thesupplying of electrical heat energy to the whole, or parts, of just thematrix, that said electrical heat energy is supplied via or immediatelybeside the outer layer belonging to the matrix and that said layerand/or the supporting layer consist(s) of an electrically conductingand/or electrically semi-conducting material.

As a suggested embodiment, falling within the scope of the inventedconcept, it is taught that the layer belonging to the matrix is selectedfrom a material with a resistivity of between 0.025 and 0.12 Ohms×mm²/m.

It is further taught that said layer belonging to the matrix issupported by a further layer with a resistivity of 0.3 Ohms×mm²/m orless.

It is further suggested that such a supporting layer should be formedfrom a heat-producing layer.

The supporting layer can also consist of a material with a higherresistivity and positioned intermediate two layers having lowresistivity.

The invention further shows that such an intermediate positioned layercan be selected to have different thicknesses, thicker at surfacesections that require low heat energy and thinner at surface sectionsthat require high heat energy.

The invention specially teaches the application of that the layer havingthe negative surface structure belonging to the matrix can have the formof a microstructure and therewith requires that the heat productionshould be adapted so that it is greater at selected surface sectionsthan at other surface sections in order to thereby increase thereplication accuracy and mould filling.

The electrical heat energy can be supplied through applying a voltage toperipheral surface parts for a selected layer.

Alternatively the electrical heat energy can be supplied throughapplying a voltage to peripheral surface parts of different layershaving low resistivity in order to produce heat within an intermediatepositioned layer having a high resistivity.

Advantages

Those advantages that are primarily afforded by a method of producing amatrix adapted for use in a compression moulding machine and/or aninjection moulding press in accordance with the present invention residein the creation of conditions which enable the matrix to be producedmore simply. In particular, this can be achieved by applying a thinfirst wear-resistant layer to the positive microstructure on one side ofa master and thereafter applying a plastic composite in order tofill-out irregularities in said wear-resistant layer and to form acarrier element.

This eliminates, or at least substantially reduces, the need to smoothdown the plastic rear surface of the matrix in order to obtain a flatmatrix surface which can abut a flat support surface of a mould body inthe machine used.

The heat transfer capacity and/or the heat capacity of the matrix canalso be adapted so as to enhance the replication capacity in theproduction process, such as the embossment process and/or the injectionmoulding process, by virtue of the fact that the forming plasticmaterial will not freeze as soon as it comes into contact with themicrostructured surface of the matrix, but is able to remain fluid foras long as it takes to replicate the matrix microstructure effectivelyon the formed plastic element.

The matrix in accordance with the present invention, enables thethickness of an applied first wear-resistant layer, such as a metallayer, to be greatly reduced, thereby reducing the production time.Additionally, through the selection of a supportive plastic compositefor forming a carrier element, an adapted carrier surface can be formed,optionally with a wear-surface reinforcement, which can also function asa heat insulator and/or a heat storage between a hot pressed plasticmass and the matrix-associated mould part.

Further advantages such as being able to, with simple measures, offer ahigher replication accuracy than previously and a more simple mouldfilling of an outer structure belonging to a plastic element, can beobtained through supplying electrical heat energy to the whole orselected parts of the matrix.

The application of heat energy to the outer structure of the matrixoccurs in the first place in order to be able to counteract or eliminatethe matrix and mould half cooling effects on the heated plastic mass,when it is squeezed in between the mould halves in the machine for themanufacturing of plastic elements.

Through the utilised and supplied electrical heat energy beingconcentrated to the outer layer of the matrix or in the vicinity thereofthe matrix and the mould halves can be given a temperature which isadapted for a quick cooling down of the plastic part by disconnectingthis supply of heat energy.

The primary characteristic features of an inventive method and theprimary characteristic features of an inventive matrix are set forthherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to an embodiment ofan injection moulding press at present preferred and in which aninventive matrix can be used, and with reference to a method ofproducing the matrix and to a matrix manufactured by said method thathas features significant of the present invention, with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic side view of part of an injection moulding pressand shows two mould halves in mutually co-operating positions;

FIG. 2 illustrates the machine of FIG. 1 in a stage of operation inwhich heated plastic mass in the form of a plastic composite is beingpressed through a fixed mould half and into a cavity formed between twomould halves, for pressure-casting or die casting of a flat plasticelement;

FIG. 3 illustrates the injection moulding press where a moveable mouldhalf has been moved away from a fixed mould half and the shaped flatplastic element has been ejected from the moveable mould half;

FIG. 4 illustrates in perspective a microstructured matrix that can beplaced in the moveable mould half, a simplified enlarged view of part ofthe microstructure also being shown in FIG. 4, although not according toscale;

FIG. 5 is a sectional side view illustrating one example of a method ofmanufacturing a prior art matrix;

FIG. 6 is a sectional side view illustrating one example of a method ofmanufacturing a matrix in accordance with the invention matrix;

FIG. 7 is a sectional view of part of a first embodiment of a matrixproduced in accordance with the invention;

FIG. 8 is a sectional view of part of a second embodiment of a matrix inaccordance with the invention; and

FIG. 9 illustrates the use of a mould cavity for producing a matrix thathas a flat rear surface.

FIG. 10 shows in a perspective view the injection moulded plane plasticelement, in the form of a CD-disk, at a distance outside the moveablemould half provided with a matrix,

FIG. 11 shows a cross-section a first embodiment of a negative surfacestructure of a matrix,

FIG. 12 shows a cross-section of a second embodiment of a negativesurface structure of a matrix,

FIG. 13 shows a cross-section a third embodiment of a negative surfacestructure of a matrix and

FIG. 14 shows a cross-section of a fourth embodiment of a negativesurface of a matrix.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED

The present invention relates to a method of producing a matrix 2, inparticular a matrix 2 adapted for use in a compression moulding,embossing, injection moulding and/or other plastic element-producingpress 1

One surface of the matrix 2 is given a negative microstructure 2 a thatcan be replicated as a positive microstructure 3 a on a plastic element3 in the injection moulding press 1.

The method by means of which the matrix 2 is produced will be describedin more detail below with reference to FIG. 6.

For the sake of simplicity, the following description assumes thatsolely the moveable mould half is provided with a matrix 2 that has amicrostructure 2 a, although the person skilled in this art will realisethat the fixed mould half may also be provided with such a matrix.

Thus, FIGS. 1-3 illustrate schematically an injection moulding press Ithat includes an ejector rod 1 a, a number (3) of ejector pins 1 b, amoveable mould 1 c and a fixed mould 1 d.

The moveable mould half 1 c and the fixed mould half 1 d definetherebetween a cavity 1 d whose shape conforms to the shape of a flat,injection moulded plastic element 3, said cavity including a cavityinlet 1 f in the shape of an intake.

FIG. 1 also illustrates the use of a “pineapple” 1 g, a cylinder wall 1h, a heating element 1 l, an injection ram 1 j and a filling funnel orhopper 1 k for granulated or powder material 1 m.

FIG. 2 shows how a heated, flowing plastic mass or plastic material 1 psurrounds the “pineapple” 1 g and is pressed through the cavity inlet 1f by the plunger 1 g and into the cavity 1 e with the mould halves 1 c,1 d brought together in the position shown in FIG. 1.

FIG. 3 shows that the moveable mould half 1 c is moved away from themould half 1 d to a given position in which the flat plastic element 3is parted from the moveable mould 1 c with the aid of the ejector rod 1a and the ejector pins 1 b, so as to fall out of the mould half 1 c.

FIG. 4 is a very simplified, perspective view of a plate-like matrix 2which includes an upwardly facing microstructure 2 a on one sidethereof.

This microstructure is normally a very complex structure. However, forthe sake of ease of illustration of the present invention, an extremelysimplified and enlarged embodiment of this microstructure is also shownin FIG. 4, but not according to scale.

For the sake of simplicity and clarity, the following description willbe concerned solely with a microstructure that includes a first raisedpart 21, an intermediate cavity or hollow 22 and a second raised part23.

The matrix 2 is thus provided with a negative microstructure 2 a on onesurface thereof.

The matrix 2 has the form of a disc or a plate that has a flatundersurface 2 b, normally a flat machined surface 2 b, which rests on aflat supporting surface 1 c′ in the moveable mould half 1 c.

It is important in this respect that the matrix has a flat (or curved)surface 2 b which is able to rest against a flat surface 1 c′ (or acomplementary curved surface) on the mould half 1 c, such that thematrix 2 will be able to withstand the pressure forces that aregenerated during the process of manufacture, for instance during aninjection press-moulding process.

FIG. 5 is a cross-sectional view of part of a known matrix 2, takenthrough the raised parts 21 and 23 and the cavity 22.

In the known method illustrated in FIG. 5, the matrix 2 can be producedby coating a surface with metal through, for example, a metal platingprocess, to provide a master that has a positive microstructure on oneside.

By means of this plating process, or corresponding process, metal layerupon metal layer are built up on the microstructure surface part 5 a ofthe master, such that a first metal layer will cover even a lowest pointin the microstructure on said surface part 5 a.

Because such a plating process will result in a metal layer whose uppersurface will be irregular owing to the underlying surface structure 5 a,it is necessary to continue the plating process and form metal layer upon metal layer until a combined thickness is reached which will exceed,over the whole of said surface, a predetermined value or plane,indicated by 6 in FIG. 5.

In the case of the earlier known method, it is necessary to grind awayall of the metal material 6 a applied over the surface 6, in one way oranother.

Plating processes for applying layers of the thickness concerned in thisrespect are very time-consuming. Grinding of the surplus metal material6 a down to the plane 6 is also very time-consuming.

According to the present invention, a matrix 2 is produced with the aidof a master 5 that may be produced in the same way as the master 5 shownin FIG. 5.

According to the present invention, the surface-carried positivemicrostructure 5 a is covered with a thin wear-resistant first layer 7,shown in FIG. 6. This thin wear-resistant first layer 7 shall present anouter first wear-resistant surface 7 a. The expression “wear-resistantsurface” is intended to mean a surface against which the hot, flowingplastic material shall be pressed and against which the plastic element3 shall be formed prior to being removed from the mould halves 1 c, 1 d.

The wear-resistant layer 7 that forms the first wear-resistant surface 7a will be sufficiently thin, for instance a thinness of 2 μm, for it toshow a negative outer microstructure 2 a that corresponds exactly to thepositive microstructure 5 a for the master 5.

The person skilled in this art is well aware of the fact that themethods and processes used in this regard will give different layerthicknesses and that it is necessary to choose a thickness and a methodwhich will ensure that the area between said raised parts will be keptopen.

The first wear-resistant layer 7 may be comprised of a plastic compositeor some other hard material, although it is assumed in the followingdescription by way of illustration that this thin, first wear-resistantlayer 7 is comprised of metal.

The metal layer 7 can be applied with the aid of conventionaltechniques, for instance by sputtering or vapour deposition against anon-conductive master plate 5.

FIG. 6 is intended to show that this thin metal layer 7 can be appliedto precisely cover the whole of the surface 5 a allocated to themicrostructure with a thin layer of metal

In accordance with the requirements of the invention, the inner or uppersurface of the thin metal layer 7 in FIG. 6 will present irregularities7 b that correspond substantially to the microstructure 5 a.

According to the invention, these irregularities 7 b are filled in asecond stage with a selected plastic composite 8′. The plastic mass usedfor this plastic composite 8′ should be hot and will be sufficientlyfluid to fill all cavities or hollows 22 and cover all raised parts 21,23 and therewith provide a flat upper surface 8 a.

FIG. 6 is intended to illustrate an embodiment in which a plasticcomposite 8′ is applied to form a carrier element 8 in a manner suchthat a small proportion 8 a′ of the plastic composite will be locatedover the plane 6 and a contemplated flat surface 8 a, wherewith theexcess plastic material 8 a′ can now be easily removed by a mechanicalplanning process.

The matrix 2, in the form of a carrier element 8 and a thin firstwear-resistant surface 7 a, is lifted out of or away from the masterunit 5 and mounted in the moveable mould half 1 c with the surface 2 b(6) in abutment with the surface 1 c′.

According to the invention, the plastic composite 8′ that is used toform a carrier element 8 may conveniently be applied under pressure in amould cavity in a manner such as to obviate the need of machining ormechanically working the rear side of the carrier element.

This third stage in the manufacturing process will be described in moredetail below with reference to FIG. 9.

The use of a plastic composite 8′ and a carrier element 8 formedtherewith affords many adaptation possibilities. It is well known thatdifferent polymeric materials and mixtures thereof admixed withdifferent fillers and mixtures thereof give different properties, andthat selected curing processes and curing times influence the finalproperties of the plastic composite. This knowledge offers manydifferent possibilities with respect to its application with a matrix inaccordance with the invention For instance, a plastic composite 8′ maybe chosen from a polymeric material that has been mixed with a fillingmaterial, such as quartz-filled, metal-filled or carbon-fibre or otherfibre or particle-filled epoxy or silicone polymers.

It is also proposed in accordance with the invention that the plasticcomposite 8′ and a carrier element 8 formed therefrom can be chosen tohave a coefficient of linear expansion or a thermal conductivity and/ora heat capacity that is adapted to a chosen process and/or to the natureof the machine used.

The plastic composite 8′ may be chosen to cure in response to heatand/or through illumination with UV-light. These curing possibilitiesmay be conveniently utilised so as to enable the plastic composite to beadapted to give the requisite hardness and stiffness.

The plastic composite used may be a bicomponent type.

FIGS. 7 and 8 are intended to illustrate that when a plastic composite8′ chosen to form a carrier element 8 located beneath the hard metallayer 7 forming a first wear-resistant surface 7 a has an adapted lowthermal conductivity (e.g. under 2 W/m/°K) and/or an adapted high heatcapacity (obtained by having a preferably high specific heat capacityand/or a large mass), the plastic composite 8′ and the carrier element 8will function as a heat insulator against the mould half 1 c, so thatthe plastic material pressed forward in the machine can be kept hot forthe length of time taken for it to flow to and fill the most distantparts of the mould in order to form the microstructure pattern 3 a inthe plastic element 3.

In order to obtain an exact microstructure-related transfer, manyapplications require the heat and the temperature of the plasticmaterial pressed into the mould to be maintained in said materialwithout heat transferring to the mould half 1 c too quickly.

According to the present invention, the matrix 2, shown in FIGS. 7 and8, is coated with or has applied thereto a second wear-resistant layer 9that provides a second wear-resistant surface 9 a. This layer 9 isapplied to the surface 8 a of the carrier element 8 that faces away fromthe metal layer 7 and may consist of a hard-wearing layer and/or aheat-insulating layer.

The second wear-resistant layer 9 shall present to the surface 1 c′ ofthe mould half 1 c a low-friction wear surface 9 a of high abrasiveresistance, since the pressure between the matrix 2 and the mould half 1c is high during the casting or moulding process and thermal stressestend to displace the matrix 2 relative to said mould half 1 c.

The second wear surface 9 may, in this case, conveniently comprisetitanium nitride or diamond-like-carbon (DLC).

In certain applications, the material used to form the second wear layer9 may be the same material as that used to form the thin, firstwear-resistant layer 7 a, with a plastic carrier element 8 placedtherebetween.

The thin metal layer 7 can be applied by a sputtering process and/or byvapour deposition, or by a plating or cladding process.

FIG. 8 illustrates an alternative embodiment which includes anabrasion-resistant second wear layer 9, a carrier element 8 formed by aplastic composite 8′ and a thin, first wear-resistant layer in the formof a metal layer 7, where a cavity or hollow 22 has the dimensions shownin FIG. 4, whereas an adjacent hollow or cavity 24 is much deeper thansaid cavity 22. A carrier element 8 having a carrier surface 8 b for thethin first wear-resistant layer 7 and/or said layer 7 may comprise aplastic composite 8′ having a coefficient of linear expansion and/or athermal conductivity and/or a heat capacity adapted to a chosen processand/or to the design of the moulding machine used. Preferably thecoefficient of linear expansion is lower than 1×10⁻⁵/°K so that themoulded structure does not change shape too much when exposed to theextremes of temperature found in plastic element manufacturingprocesses.

The carrier element 8 may also be comprised of a plastic composite thatcan be given different degrees of hardness, by applying differentdegrees of heat and/or by irradiation with UV-light.

The carrier element 8 may also be comprised of a material that has a lowthermal conductivity and a high heat-insulating and/or heat capacity inorder to prevent it absorbing too much heat energy from the hot plasticmass.

The carrier element 8 may also be reinforced with known means. Forinstance, the carrier element 8 may be strengthened with a furtheranti-wear layer 9 on the surface thereof that lies distal from themetalled surface 7.

Although the invention has been described above with reference to anembodiment in which a thin wear-resistant layer 7 is supported by athicker plastic layer or carrier element 8, it is suitable in certaincases to form these two wear-resistant layers from one and the sameplastic material.

There is nothing to prevent the wear-resistant layer 7 from curingfirst, preferably to a high degree of hardness, and curing thesupportive plastic layer or carrier element 8 at a later time to a lowerdegree of hardness.

As illustrated in FIG. 9, the plastic composite 8′ may be applied to amould cavity 90 in the form of a casting matrix or mould 91 with the aidof an overpressure exerted by a plunger 92, so that the surface 8 a ofthe carrier element will be made flat by the surface section 91 a of themould 91.

This flat surface 8 a can now be applied directly to the support surface1 c′ of the mould half 1 c.

With regard to the thickness of the layer 7, a basic rule is that thethickness will be sufficient to prevent a collapse or crack formationoccurring during a chosen number of casting or moulding processes. Thismeans, in practice, a thickness of 1-5 μm.

More generally, the thickness may range between 1 and 50 μm, and willpreferably be less than 20 μm.

In certain applications, however, the layer may have a thinness of about0.1 μm, depending on the material from which the carrier element 8 isformed, among other things.

The thickness of the wear layer 9 may be between 1 and 50 μm, preferablyless than 20 μm.

The depth variation of the microstructure 1 a may vary between 0.1 and1000 μm, and will preferably be above 100 μm.

In a further embodiment of the present invention, the matrix 2 isprovided with means for improving the replication of its microstructure2 a on the plastic element 3. As mentioned above, the matrix 2 in aknown way is provided on one surface with a layer 7 having a negativesurface structure 2 a and against which negative surface structure 2 a apositive surface structure 3 a belonging to a plastic element 3 isformed.

The manufacturing of the plastic element 3 occurs principally throughthe mould half 1 c and 1 d taking up a joined together position andthereby forming said mould cavity 1 e. Before the moulding sequence, themould halves 1 c and 1 d are heated in order to facilitate thedistribution and the filling of the mould cavity 1 e by a heated plasticmass (approximately 400° C.).

Normally the mould halves 1 c and 1 d and the matrix 2 are given aconsiderably lower temperature than the plastic mass and there is a riskthat a hot (say approximately 400° C.) plastic mass does not manage tofill the mould cavity 1 e and flow out to the edges before the plasticmass solidifies against the surface 2 a of the matrix 2. Subsequentlythe plastic mass is cooled so that at least the surface structure 3 a ofthe plastic element is solid (say approximately 140° C.) and then themould halves 1 c and 1 d are opened and the plastic element ejected (inaccordance with FIG. 3). In practice, the method requires a rapidtemperature change and the cycle times for the manufacture of plasticelements 3 are strongly dependent on the speed and the efficiency ofthis temperature changing.

The present invention is based upon that a required heating shall takeplace in the surface structure belonging to the layer 7 of the matrix 2or in a layer situated close to this layer and especially that thenecessary heating should be able to be concentrated to the parts where arisk for a incomplete filling is specially imminent with increasedproduction speed.

The invention now suggests that the used mould halves 1 c and 1 d, andalso a part of the matrix 2, shall through having a more or lessconstant application of cooling means be given a comparatively lowtemperature in order to be present as an available cooling capacityimmediately after the end of a moulding process. The lower that thistemperature is, the quicker the cooling, but in practice a temperatureof 80° C. is preferable with a plastic solidification temperature of140° C. In practice, a suitable temperature difference between thesolidifying temperature of the plastic material and the temperature ofthe mould halves should be between 40-100° C., such as approximately50-70° C., in an application in accordance with the present invention.

The whole of the layer 7 of the matrix 2 or in any case one or morelocal parts thereof shall be preheated via an electrical production ofheat to a suitable moulding temperature immediately before thecommencement of the moulding process.

In practice, it is so that the layer 7 is heated up by the hot plasticmass when this plastic mass is injected into the mould cavity. In theregion around the cavity inlet 1 f, the region 21 a, the injectedplastic mass 1 p will keep the layer 7 hot so that a complete fillingwill take place despite the cooling effect of the matrix layer 7. Formore peripheral surface sections, such as the region 21 b, the injectedplastic mass 1 p will have been cooled down by the layer 7 and it iswithin this region that a incomplete filling occurs because of anextremely thin plastic layer, a skin layer, solidifying against thelayer 7 of the matrix 2. It is in order to eliminate the occurrence ofsuch skin layers 1 s that the present invention relates to a localheating of the layer 7 of the matrix 2 in at least the region 21 b.

The layer 21 b of the matrix normally does not need to have a very hightemperature from the local heating and a temperature around or somethingover the actual solidification temperature is normally sufficient. Theinvention can however offer a temperature for the region 21 b of thelayer 7 which can be up to an extremely high temperature, say over 200°C.

The arrangement belonging to the matrix in accordance with theinvention, is further based upon the use of a heating means 4, in orderto, in the first instance, for a short duration of time, supply saidmatrix 2 and/or the selected region (21 b) with a requisite heat energy.

The necessary cooling can take place through keeping the mould halves 1c and 1 d constantly cold via a (not shown) cooling means.

The invention can be considered such that immediately before, andpreferably during, the moulding process the electrical heat energyshould be supplied to form a thin heat layer between the matrix surface2 a and the mould half 1 c in order to facilitate good filling of themould by the hot plastic mass.

When the electrical heat energy is disconnected the matrix surface 2 aand the layer 7 are quickly cooled down to a temperature below thesolidifying point for the plastic mass through the low temperature whichis being selected to be in force on the mould halves rising up throughthe layer 7 and the hot plastic element 3 present in the mould cavity 1e. In this way, the cycle time for the manufacture of each such plasticelement 3 is reduced.

FIG. 10 shows that the one connection wire 4 a of the heating means 4 isconnected to the outer peripheral edge 2 b of the matrix 2 and the otherconnection 4 b is connected to the central edge 2 c of the matrix asconnection points 2 b′ respectively 2 c′.

It is assumed that these connection points 2 b′ and 2 c′ are connectedto the layer 7 which can be electrically conducting or to one or moreunderlying layers such as 31, 41, 42 and 52 which can be electricallyconducting or semi-conducting.

With reference to the FIGS. 11-14 the present invention's specificcharacteristics will now be closely illustrated through describing anumber of different materials and constructions for the negative surfacestructure 2 a of the matrix 2 and the layer 7 with the adjacentunderlying layers.

The following description comprises for the sake of simplicity only thelayer 7 and a number of layers belonging to the matrix situated close tothis layer.

Heating means 4 referred to in accordance with the invention is thesupply of electrical heat energy to the whole or selected parts of thematrix 2 and directly or indirectly to the layer 7, and via a switchingmeans (not shown) heat energy is supplied immediately before and duringthe injection moulding process in order to keep the walls of the matrixhot and thereby facilitate that the hot plastic mass flows out.

The connection shown in FIG. 10 for manufacturing a circular disk 3(e.g. a compact disc) implies a higher current density and a higher heatemission from the surface part 21 a of the layer 7 adjacent the centraledge of the hole 2 c than within the peripheral edge 21b and the surfaceregion 21 b.

This condition actually counteracts the primary necessity since afurther heating of the surface part 21 a can hardly be considerednecessary.

Heating up of the part of the surface 21 b is on the other handnecessary. A first possibility for this is offered by overheating thesurface section 21 a in the aid of an adapted heat supply to the surfacesection 21 b when layer 7 is essentially evenly thick.

Another possibility is to allocate different thicknesses to the layer 7with a thinner layer across the direction of current in the surfacesection 21 b than in the surface section 21 a and with a thereofguaranteed increased heat development in the surface section 21 b.

Preferably said electrical heat energy is applied via or immediatelynext to the layer 7 of the negative surface structure 2 a belonging tothe matrix and FIG. 11 illustrates an embodiment where the electricalheat energy can be supplied only via the thin layer 7 of the surfacestructure 2 a.

The optimal thickness of the layer 7 depends on the selectedmanufacturing process, selected plastic material, design of the matrix,selected concentrated heat production within the selected partialregions and many other criteria. Practical experience shows that in manyapplications the thickness should be selected to be less than 20 μm, say2-10 μm, or up to 5 μm.

With the electrical connections shown in FIG. 11, if layer 7 is made ofjust one type of material then more heat will produced in the centralpart 2 c while a lesser energy production will occur in the peripheralpart 2 b due to the differing current densities. Such an embodimentshould possibly be especially suitable if the microstructure around thecentral edge 3 c in the element 3 is sensitive to the mouldingconditions and, therefore, in order to obtain a good replicationcapacity and mould filling, a higher temperature of the plastic mass andthe matrix is required there than in the peripheral region.

A suitable precondition for the present invention is furthermore,according to FIG. 11, that said layer 7 having the negative surfacestructure 2 a and/or a layer 31 supporting this layer 7 consist(s) of anelectrically conducting or electrically semi-conducting material.

When connected in accordance with FIG. 10 the connection points 2 b′ and2 c′ can be connected to just layer 7, just layer 31 or to both layers 7and 31. The layer 31 can consist of an electrically conducting polymer.The layer 7 having the negative surface structure belonging to thematrix is preferably made of a material, such as nickel, with aresistivity of between 0.025 and 0.12 Ohms×mm²/m.

The local heat production across the direction of the current flow canbe regulated through locally changing the thickness (and consequentlythe cross-sectional area) of the layer 7, with a thinner layer ofmaterial where a higher heat production is required and a thicker layerof material where a lower heat production is required. Regard should bepaid to the current density occurring in the material to prevent itbeing damaged.

Said layer 7 having the negative surface structure belonging to thematrix is, in FIG. 12, supported by a layer 41 with a resistivity of0.03 Ohms×mm²/m or less. The thickness of the layer 41 should beselected depending on the relevant criteria, in the same way as for thelayer 7. Practical experience shows that in many applications thethickness should be selected to be less than 20 μm, preferably thinnerthan 10 μm and advantageously up to 5 μm. The layer 41 canadvantageously be made of gold, silver or the like.

A further supporting layer 42 can be formed of a heat producing and/orsupporting layer, where said supporting layer 42 can consist of amaterial with high resistivity. An electrically conducting polymer canalso be used here.

FIG. 13 shows a layer 52 having a high resistivity intermediatelypositioned between two thin layers 41, 51 that each have a lowresistivity.

FIG. 13 also shows that the layer 7 can be the same as the layer 7according to FIG. 11, that the layer 41 can be the same as the layer 41in FIG. 12 and that a supporting layer 42 can be formed from the furthersupporting layer 52. It is especially advantageous that the layer 52 canhave different thickness (i.e. varying cross-sectional areas), thickerat sections which require low heat energy and thinner at sections whichrequire higher heat energy. In this embodiment, the voltage from theheating means 4 is connected to layers 41 and 51.

The invention has a special application where the layer 7 having thenegative surface structure 2 a belonging to the matrix has the form of amicrostructure 2 a and this microstructure 2 a is to be transferred tothe plastic element 3 as a positive micro-related surface structure 3 a.In this application it is especially important to allow the heatproduction to be adapted to be higher at some selected surface sectionsbelonging to the matrix than at other surface sections in order tothereby increase the replication accuracy and degree of mould filling ormould filling capacity.

FIG. 14 shows a further embodiment of the present invention. Thepractical application here also requires dimensional variations withinwide ranges. The thickness of the layer 7 should be selected to be lessthan 10 μm, say 2-8 μm. As an example, the layer 7 here consists of upto 5 μm thick titanium nitride which gives a hard surface 21 arespectively 21 b against the plastic element 3 and has good wear—andrelease characteristics. The layer 41 can consist of an up to 300 μmthick nickel layer that gives a hard coating and forms a support andcarrier for the layer 7. Nickel is relatively cheap and can beconsidered to have acceptable electrical conductivity. The layer 61should consist of a material with good electrical characteristics suchas gold, silver, copper. The thickness of this layer should be thin, sayless than 10 μm, for example 2-8 μm and preferably under 5 pm. Thesupporting layer 62 can be made of a polymer material which can beplated and which acts as a heat shield. These layers can be appliedadvantageously with known techniques such as surface deposition,plating, casting, spinning, spray painting or via vacuum depositiontechniques such as sputtering or vaporisation.

It will be understood that the invention is not restricted to thepresent described and illustrated exemplifying embodiments thereof andthat modifications can be made in accordance with the concept of theinvention as defined in the accompanying claims. Furthermore, featuresshown in the individual embodiments described above may be combined withfeatures from other embodiments, thus, for example, the heating means ofthe present invention may be combined with any suitable layers andcarrier elements of the present invention.

1. A matrix for use in the replication of a plastic element having apositive microstructure, comprising a first wear-resistant layer,wherein said layer is supported by a carrier element having a thermalconductivity of less than 2 W/m/°K, wherein said layer consists of anelectrically conducting or semi-conducting material having a resistivityof between 0.025 and 0.12 ohms×mm²/m, wherein said matrix is in the formof a singular structure mould cavity insert and is connected to a sourceof electrical heat energy via the first wear-resistant layer or a layersupporting the first wear-resistant layer by a connecting means.
 2. Thematrix of claim 1, wherein the carrier element has a resistivity of lessthan 0.3 ohms×mm²/m.
 3. The matrix of claim 1, wherein the carrierelement has a resistivity of less than 0.03 ohms×mm²/m.
 4. The matrix ofclaim 1, wherein the carrier element is capable of producing heat. 5.The matrix of claim 1, wherein the electrical heat energy is supplied byapplying a voltage to the electrically conducting or semi-conductingmaterial of the first wear-resistant layer.
 6. A plastic elementproducing machine including the matrix of claim 1, wherein said machineis a compression moulding, an injection moulding or an embossingmachine.
 7. A method for the manufacture of a plastic element having asurface with a positive microstructure comprising the steps of: (i)providing the matrix of claim 1; and (ii) replicating said plasticelement on said matrix while supplying heat energy to the electricallyconducting or semi-conducting material of the first wear-resistant layerduring the filling of the matrix mould cavity with molten plastic. 8.The method of claim 7, wherein step (ii) is performed in a plasticelement-producing machine based on replication of the matrix.
 9. Themethod of claim 8, where said plastic element-producing machine is acompression moulding, an injection moulding or an embossing machine. 10.The method of claim 8, wherein said first wear layer is a metal layer.11. The method of claim 8, wherein said plastic element is an opticaldisc.
 12. The matrix of claim 1, wherein said carrier element comprisesa polymer material that acts as a heat shield.
 13. The matrix of claim1, wherein said carrier element comprises a plastic composite.
 14. Thematrix of claim 1, wherein said first wear-resistant layer has athickness ranging between 1 and 50 μm.
 15. The matrix of claim 1,wherein said first wear-resistant layer is a metal layer.
 16. The matrixof claim 1, wherein said first wear-resistant layer exposes an inversemicrostructure on its surface having a depth variation ranging between0.1 and 1000 μm.